General Description: If a DCM is driving multiple global buffers on the same edge (top or bottom) of the chip, there is a placement restriction that is currently not being checked.
There are pairs of buffers with shared dedicated routing resources such that if both are driven by the same DCM, one of the two will necessarily be driven using non-dedicated routing resources; this may cause the design to not work.
If the buffers are numbered 1 through 8 from left to right, there are 4 pairs of exclusives: 1:5, 2:6, 3:7, 4:8. If a buffer is placed in site 1, another driven by the same DCM may not be placed in site 5.
This problem will be fixed in the first 4.1i service pack, due out in late September, 2001
Meanwhile, the work-around is to manually constrain the BUFGMUX site locations.